Image sensor arrays typically comprise a linear array of photosensors which raster scan an image bearing document and convert the microscopic image areas viewed by each photosensor to image signal charges. Following an integration period, the image signal charges are amplified and transferred as an analog video signal to a common output line or bus through successively actuated multiplexing transistors. A basic circuitry for such an image sensor array is given in U.S. Pat. No. 5,081,536, the disclosure of which is incorporated herein by reference in its entirety.
A desirable feature of a photosensitive apparatus having an array of photosensors is the capability for multiple selectable imaging resolutions. For example, if a chip includes a set of photosensors spaced 600 to the inch, it may be desirable to operate the chip so that each adjacent pair of photosensors in effect operates as one photosensor, so that the effective spatial resolution of the apparatus is 300 spots per inch. A lower spatial resolution results in smaller image file sizes (which may be desirable in some scanning contexts, such as archiving, or pattern or character recognition) and can facilitate a higher readout rate.
FIG. 7 is a block diagram of prior art sensor array 400. Each pixel in the sensor array is connected to a pixel amplifier which is connected to one of video lines VIDO or VIDE. The amplifiers are connected in an alternating sequence to one of an odd or an even pixel shift register 402O or 402E. The odd pixel registers are activated on a rising pulse from the CLK input and the even pixel registers are activated on a falling pulse from CLK. The PXO and PXE outputs from the registers activate a video line switch for a respective pixel amplifier so that the respective pixel amplifier transmits to a respective video line. Thus, the prior art teaches a sensor array which operates at a fixed resolution dependent upon the configuration of the pixels, and has a fixed readout time, linked to the resolution. For a desired resolution reduction, the prior art teaches producing image data with unnecessarily high data rates and then adjusting resolution by processes outside of the sensor array. Thus, all of the pixels are readout and processed even though only a portion of the pixels are actually needed for the desire resolution.
U.S. Pat. No. 6,958,833, the disclosure of which is incorporated herein by reference in its entirety, describes the operation of shift registers in a sensor array, for example, describing a photosensitive apparatus including a plurality of photosensors organized in a set of groups of photosensors, and a video output line for accepting image-related video signals from the photosensors. Selection means activate a subset of groups of photosensors so that only the activated subset of groups of photosensors outputs image signals onto the video output line to record an image.
U.S. Pat. No. 7,471,327, the disclosure of which is incorporated herein by reference in its entirety, describes a photosensitive imaging apparatus with a linear array of groups of photosensors. In a low-resolution scanning mode, all of the photosensors in each group act together as one large photosensor. In a high-resolution scanning mode, each photosensor in a group acts outputs image-based signals independently. In either mode, the signals output by the photosensors are transferred to one of two output lines, such as for “odd-” and “even-” positioned photosensors or groups of photosensors. The signals on the two lines can then be multiplexed to a single output line. The dual output lines enable fast signal output in either resolution mode.